1.
mag-
‘ritual’ to make a vow
not
do
something.
In this ceremony, an animal is sacrificed and is overseen by an imam .
You make a vow now, you say, "I shall not [do it] again now."
2.
to promise
not
to
do
something again; hence, to repent.
This is the sense most often used now-a-days. Animal sacrifice is not necessary in promising.